Bush: 'Our entire nation grieves' for astronauts 'The cause in which they died will continue' WASHINGTON (CNN) --Seven astronauts who died aboard space shuttle Columbia on Saturday were saluted for "their courage and daring and idealism," as shocked Americans mourned the lives lost in the third fatal disaster in the U.S. space program's storied history. "Columbia's lost. There are no survivors," a grim-faced President Bush said in an address to the American people. "These astronauts knew the dangers, and they faced them willingly, knowing they had a high and noble purpose in life." Bush ordered flags on federal buildings lowered to half-staff until Wednesday in honor of Columbia's crew, and many state governors followed suit. "This day has brought terrible news and great sadness to our country," the president said during the address. To the families of the astronauts, Bush said, "Our entire nation grieves with you," and he made it clear that the United States would continue with manned space flight, despite the risks. "The cause in which they died will continue," he said. "Mankind is led into the darkness beyond our world by the inspiration of discovery and the longing to understand. Our journey will go on." After naming the seven astronaut aboard the shuttle, Bush said, "These men and women assumed great risk in service to all humanity. In an age when space flight has come to seem almost routine, it is easy to overlook the dangers." For their courage and idealism, "we will miss them all the more," he said. "All Americans today are thinking as well of the families of these men and women," Bush said. "Our entire nation grieves with you. And those you loved will always have the respect and gratitude of this country." Those killed on the ill-fated flight included six Americans: Rick Douglas Husband, Michael P. Anderson, William C. McCool, David M. Brown, Laurel Salton Clark and Kalpana Chawla, a native of India. Also on board was Ilan Ramon, a colonel in the Israeli air force who was the first citizen of his country to fly in space. The Columbia was returning to Kennedy Space Center in Florida after a 16-day research mission when it broke up in flames about 200,000 feet over north-central Texas minutes before it was scheduled to land. NASA officials at the Johnson Space Center in Houston, Texas, said they last had contact with the craft about 9 a.m. EST. At a news conference from Kennedy Space Center in Florida, NASA Administrator Sean O'Keefe said he had contacted Bush and Homeland Security Director Tom Ridge shortly after the shuttle did not arrive for its scheduled 9:16 a.m. landing. O'Keefe said Bush offered his "full and immediate support." O'Keefe then met with family members of the astronauts, and he said the president called them to offer the "deepest national regrets." Bush cut short his weekend at Camp David to return to the White House to meet with his chief of staff and top advisers. According to a senior administration official, the president learned of the shuttle disaster at about 9 a.m. EST from White House Chief of Staff Andrew Card, who was also at Camp David. The official said that while the president was receiving his usual intelligence briefing, Card was watching NASA Television, awaiting the shuttle landing, when he saw that NASA had lost contact with Columbia. Card alerted the president. The official said Bush's first reaction was "deep concern for those on board, especially for the families." After a telephone briefing by O'Keefe, the president returned by motorcade to the White House. He was briefed again by O'Keefe, who told Bush that the families were "holding up exceptionally well ... they are a courageous group of people." Bush told O'Keefe that "this was a tough day for all." Bush consoles families Standing at his desk in the Oval Office, Bush placed a conference call to the families of the astronauts, who had assembled in a conference room at Kennedy Space Center. In the conversation, which took place on a speakerphone, Bush said, "I express my love and appreciation for all who died today. I want their loved ones to know there are millions of people praying for you ... me and Laura. I hope that brings some comfort to you. This was an incredibly tough day. May God bless you all. I wish I was there to hug, cry and comfort you. God bless you all. God bless." O'Keefe was on the other end of the phone. Afterward, Bush met with top advisers, including national security adviser Condoleezza Rice, Vice President Dick Cheney and Ridge, and then called Israeli Prime Minister Ariel Sharon to offer condolences for the loss of the Israeli astronaut. Sharon called Ramon's death a "heavy tragedy" for his nation. "These times strengthen the feeling of common destiny, values and common vision of the American and Israeli nations. Ilan Ramon and his friends on the space shuttle were victims of science, the progress and aspiration of all of us to a better life on Earth," he said in a statement. After speaking with Sharon, Bush returned condolence calls from Mexican President Vicente Fox, French President Jacques Chirac, Russian President Vladimir Putin and Canadian Prime Minister Jean Cretien. Iraq was discussed in none of those calls, the official said. Between the calls, Bush prepared to address the nation.